1. Field of the Invention
The present invention is related to temporal analysis of medical images and, in particular, to the analysis of chest radiograph images using automated temporal subtraction.
2. Discussion of the Background
For the interpretation of chest radiographs, radiologists commonly compare a current film with previous films in order to facilitate the detection of abnormalities on chest radiographs, such as pulmonary nodules, interstitial infiltrates, pleural effusions, and cardiomegaly. However, it is a difficult task for radiologists to identify subtle interval changes on chest radiographs because lesions can overlap with anatomic structures such as ribs, vessels, heart, and diaphragm. In order to assist radiologists in their evaluation of temporal changes in chest radiographs, investigators at the University of Chicago Department of Radiology have developed a temporal subtraction scheme based on a nonlinear geometric warping technique. [1] In this scheme, the subtle changes and/or newly developed abnormalities on chest radiographs were enhanced on the subtracted image. In fact, in an observer test, the detection accuracy of interval changes in chest radiographs was improved significantly by use of temporal subtraction images. [2] In a more recent study, the temporal subtraction scheme has been improved by an initial image matching technique which is based on the cross-correlation of a pair of blurred low-resolution images for determination of accurate global shift values. [3] However, misregistration errors caused by failure in local image matching were still observed in some cases.